1. Field of the Invention
This invention relates to a device for accurately measuring end play between a vehicle wheel and a wheel axle or wheel-support spindle.
2. Description of Prior Developments
Axial end play between a wheel hub and shaft must be carefully set within close tolerances in order to properly preload a pair of axially spaced wheel bearings which rotatably support the wheel on the shaft. If the end play is insufficient, the wheel bearings will experience excessive axial compression force which results in the generation of excessive frictional heat within the bearings. This heat can damage the wheel bearings and significantly shorten their useful life.
If excessive axial end play exists between a wheel hub and its shaft, the hub will slide axially over the shaft so that the oil or grease seals which are mounted to the hub and which retain lubricant around the wheel bearings may be unable to maintain an effective seal with the shaft. That is, the elastomeric seal lips which are designed for rotary contact with the shaft may be prematurely worn by the linear axial motion associated with excessive end play. In this case, lubricant may leak out from the bearings thereby resulting in excessive bearing friction and heat. This can lead to premature bearing failure.
The axial end play between a vehicle wheel and axle is typically set by torquing a nut onto the threaded end of the axle so as to apply an axial force against the end face of the wheel bearing. This procedure clamps the wheel onto the axle in a known fashion. By specifying a predetermined torque applied to the nut, such as for example, 250 foot pounds, it is generally felt that the resulting wheel end play will fall within acceptable limits. However, no tool or measuring device is presently known which can be used to measure this end play with any accuracy. In the case of truck fleet manufacture, maintenance and repair, where large numbers of wheels are assembled on axles, it would be helpful to have a tool to sample check certain wheels to assure that the correct amount of wheel end play is present.
Thus, a need exists for a measuring device which can accurately measure end play between a wheel hub and wheel axle such as found on large trucks and semis so that both the lubricant seals and the wheel bearings may function properly throughout their entire expected design life.
One type of end play measuring device is disclosed in U.S. Pat. No. 3,110,957 issued to W. Culbertson. The device shown in the Culbertson patent includes a mounting plate securable to a gear transfer case. A connector nut is threaded onto the threaded end of an output shaft for the gearing located within the transfer case. The nut is attached to a threaded rod that extends through a thrust plate spaced away from the mounting plate. Two additional rotary nuts are threaded onto the rod adjacent opposite faces of the thrust plate.
Wrench force selectively applied to the nuts causes the rod to exert a pushing or pulling force on the output shaft, thereby producing an end play between the output shaft and its support bearings within the transfer case. A dial indicator has a deflectable stem engaged with an end face of the threaded rod to measure the end play achieved by axial motion of the rod.
A device built according to the teachings of the Culbertson patent should have precision parallelism between the mounting plate and the thrust plate. Also, the threaded rod should have a precise axial orientation relative to the threads in the attached connector nut. The rigid construction of the measuring device components may compromise the ability of the measuring device to adapt to misalignments in the work being measured, i.e. the gear transfer case.